High-Field Spin Dynamics of Photoexcited Pentacene at 9.2 T by Time-Resolved Pulsed EPR and Vector DC Magnetic-Field Sensing

Photoexcited triplet spin states of pentacene molecules are promising for dynamic nuclear polarization (DNP) and quantum sensing, yet their spin properties at high magnetic fields remain largely unexplored. Here, we study the high field spin dynamics of the photoexcited pentacene using high-frequency time-resolved pulsed electron paramagnetic resonance (EPR) at 260 GHz (∼9.2 T). Using pulsed EPR synchronized with optical excitation, we determine triplet sublevel populations, decay rates, spin relaxations, and the g-tensor. The transient triplet remains a strongly non-Boltzmann sublevel population, with a dominant |TX⟩ population of 0.86 ± 0.05, while the triplet lifetimes, spin–lattice relaxation, and coherence remain favorable for triplet dynamic nuclear polarization (triplet-DNP) and quantum sensing applications. We further develop a vector DC magnetic-field sensing protocol that combines the transition resonances of the two crystallographically inequivalent pentacene sites with orientation-dependent triplet decay to determine the field magnitude and orientation. These results establish the high-field spin properties of photoexcited pentacene and provide a foundation for triplet-DNP and quantum sensing at high magnetic fields.